1. Field of Invention
The present invention generally relates to a metal-gas cell battery. More particularly, the present invention relates to a primary zinc-air battery.
2. Description of Related Art
The growth in use of portable electronic devices has increased the demand for primary power sources. The alkaline Zn—Mn battery is the most popularly used primary battery at present. Nevertheless, due to its low specific energy, it is not suitable to be used as the power source of the most portable electronic equipment, such as military communication devices. Therefore, LiSO2 and LiMnO2 primary batteries are used instead, but these batteries are very expensive. As electronic equipment becomes more and more ubiquitous, the demand for environmental friendly primary batteries with both high specific energy and high specific power is more and more pressing.
Among all of the battery technologies, metal-air batteries are the most attractive technology because of their high specific energy. Metal-air batteries deliver the high specific energy due to the use of atmospheric oxygen as their cathode reactant. Compared to other batteries of similar size, the use of atmospheric oxygen allows the metal-air cell to contain more anode material to provide a larger energy capacity. Therefore, a longer lifetime is obtained.
Among the metal-air batteries, the zinc-air battery technology is the only commercialized technology. Since the last century, the zinc-air button battery has been extensively used for entertainment electronics, pocket calculators and especially hearing aids. However, it can't be extensively used in other high-drain electronic devices due to its relatively low specific power.
Many companies and institutions wish to develop a primary zinc-air battery of AA or AAA size, which have both high specific energy and high specific power. This battery would have nearly three times the energy of an ordinary alkaline Zn—Mn battery. Many prototypes have been made successfully, but no company has yet succeeded in commercialization. The obstacle is the complicated manufacturing process of the cylindrical-shaped air cathode.
Two methods have been used to fabricate the cylindrical-shaped air cathode. The first method is to prepare the air cathode as a flat sheet and then roll it into a cylinder, as shown in U.S. Pat. No. 6,461,761. However, the rolling process may crack the air cathode, resulting in the leakage of electrolyte and failure of the cell. The second method is to fabricate the cylindrical-shaped air cathode by putting the necessary materials onto a cylindrical-shaped electrically conductive mesh. However, this is a very difficult and slow process, and the high manufacturing cost incurred leads to failure in competing with ordinary alkaline Zn—Mn battery.